


Asylum for Two

by hyliank8



Category: Undertale (Video Game)
Genre: (though maybe not the one that would be expected 🙈), Creepy W.D. Gaster, Doctor/Patient, Evil W. D. Gaster, Implied Sexual Content, Implied/Referenced Rape/Non-con, Insane Asylum AU, Insane Gaster AU, M/M, Non-Consensual Drug Use, Power Imbalance, Sans suffers, Sanster Week 2021, SansterWeek2021, W. D. Gaster is not related to Skelebros, syringes, what more could you want
Language: English
Status: Completed
Published: 2021-03-06
Updated: 2021-03-06
Packaged: 2021-03-12 22:34:02
Rating: Mature
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 1,062
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/29891541
Author URL: https://archiveofourown.org/users/hyliank8/pseuds/hyliank8
Summary: Dr. W. D. Gaster suffers from insanity after an important experiment goes awry.  Dr. Sans Serif is one of the doctors assigned to attend to him.Sans is in way over his head, even if he doesn't realize it yet.  But that's okay; Gaster is happy to acquaint him with this fact.(For day 7 of Sanster Week 2021:Surface/AU)(And also for 3/6 Sanster Day :D)
Relationships: W. D. Gaster/Sans
Comments: 21
Kudos: 24





	Asylum for Two

**Author's Note:**

> thank you to [@cui_zysr](https://twitter.com/cui_zysr) on twitter for this inspiration!! inspired by their art from [here](https://twitter.com/cui_zysr/status/1362763574213414914?s=20) and [here](https://twitter.com/cui_zysr/status/1361459787372789760)
> 
> i dunno if this could work with what they have in mind for this AU, but i have their art to thank for this fic regardless ;p
> 
> and my good friend sec was kind enough to translate the art for me :)) bc i don't actually know any chinese 😭💔

“Mm, are you here for my midnight injection, doctor?” Gaster smirks at the small skeleton as he walks into Gaster’s “private room”—though it’s much closer to a holding cell, the way it’s always locked, closed off to the rest of the world.

The doctors say they keep him in this room to keep him from wandering and getting himself hurt, but Gaster knows that’s a lie. _They_ are the ones who need to be protected from _him_ , and they know it.

“yes, doctor gaster,” Sans says, professional as ever despite Gaster’s playful tone. The door shuts behind him, the automatic lock immediately clicking into place.

Sans approaches where Gaster sits on the edge of his bed, syringe in hand with his eyes set intently on whatever forms are on his clipboard. Gaster notes with mirth the way Sans’ hands hesitate ever-so-slightly as they flip through the papers, clearly trying to make himself look preoccupied.

It doesn’t fool Gaster. It’s easy to see the effect he has on the smaller monster, no matter how much Sans may try to hide it. As Sans comes to a stop close beside him, Gaster can clearly see the beads of nervous sweat forming on his skull.

“Why don’t you let me ask you something first, from one doctor to another,” Gaster says cordially, as though he’s talking to an old friend. “Do you know what is in these vials? What it is that you’re preparing to give me all the time?”

“of course i do,” Sans replies, glancing up for a moment from his clipboard. “i’m not the most high-ranking doctor here, but i still know your injections are magic suppressors. anyone who administers your medication will know what it is.”

“Ah—do you know why, though?” Gaster counters, the smirk on his face growing. “Do you know why they suppress my magic?”

That seems to finally catch Sans off guard the tiniest bit, his professional facade slipping ever-so-slightly. Gaster latches onto the uncertain microexpression that furrows Sans’ brow, his soul beat picking up its pace at the intoxicating sign of perturbance before it disappears as quickly as it came.

“it’s because you have trouble sleeping with your overactive magic, sir,” Sans explains coridally, as though Gaster asked for his own sake—but it’s clear that he’s making an effort to speak as evenly as he can. “if you’re unhappy with your current treatment, i can bring in the specialist to speak with you. i only want to help you, doctor gaster.”

“That is true, yes,” Gaster ignores the offer, “but that’s not the only reason...” He trails off, watching Sans’ face. The small doctor glances back down at his clipboard uncertainly for a moment, but it doesn’t hide the fact that he’s entirely captivated by Gaster’s words.

“They’ve seen me looking at you and they’re... concerned with the way I watch you.”

Sans’ idle fiddling with the papers on his clipboard freezes. His jaw unhinges for a moment as though he’s preparing to say something, but he snaps it back shut as his words apparently escape him.

“You haven’t given me my dose in a while, have you, Doctor?” Gaster continues smoothly, not giving Sans an opening to reply.

“u-um,” the small doctor’s stutter sends a warm shiver down Gaster’s spine as he apparently forgoes a reply to Gaster’s previous revelation. “no, but you know that—that doctor anthony has been giving them to you instead for the past few days.”

Gaster hums, averting his gaze as he pretends to mull this over, as though deciding whether or not he agrees with what Sans undoubtedly believes to be fact. After a moment of pause, he looks back over at Sans, catching his nervous gaze.

Violet magic flares in Gaster’s pupil.

“Are you sure about that?”

Before Sans has a chance to understand, a large magic hand unfurls in front of his face and clamps over his mouth, muffling his startled yelp. In the same instant, two more materialize at his wrists and grab them, yanking them forward as the clipboard and syringe both clatter noisily to the floor.

Sans’ eye sockets have gone wide, and the startled terror in his expression burns pleasantly in Gaster’s soul. Gaster pulls him closer by his wrists until their faces are inches apart. He breathes in deeply, savoring the taste of his captive’s fear in the air surrounding him.

Sans begins to struggle in his powerful grip as the shock-induced paralysis fades, a muffled cry coming from behind Gaster’s comparatively enormous hand as Gaster’s arms wrap around his back, lifting the helpless monster onto his bed. Sans’ terrified whimper is still stifled by Gaster’s grip when the larger monster’s extra hands pin his wrists against the mattress.

“Shh, shh...” Gaster croons. “It’s alright, Doctor... it’s just the nighttime shift, right? Surely someone will notice your absence within a few hours...”

As he speaks, Gaster’s auxiliary hand fetches the dropped syringe as he moves his body over Sans’. The smaller monster’s panic increases as he realizes that he’s been hopelessly trapped between his patient and the medical bed, and Gaster’s soul flutters with excitement as he feels him desperately reach for his magic. 

Sans doesn’t get a chance to cast an attack. Gaster has decades of experience over him both as a doctor and as a fighter, and before Sans can prepare a defense Gaster has already located that vulnerable line of intangible magic on Sans’ neck and has plunged the syringe into the pliable bone.

Sans makes a sound that likely would have been a cry of pain if his voice was not still muffled by Gaster’s hands. The effect of the drug is nearly instant; Gaster feels the weak soul beneath him shudder as his victim loses his hold on his voluntary magic. Gaster knows from experience that it’s jarring to suddenly lose access to such an intimate part of oneself, and he can’t help but grin with satisfaction for a moment as he feels the small doctor helplessly continuing to reach for his magic, only for it to slip just out of his grasp again and again.

Gaster leans in close until his lips brush the side of Sans’ skull, the powerless monster flinching at the intimate contact. 

“But,” Gaster’s voice is a dangerous whisper, “we can certainly have some fun until then, don’t you think?”

**Author's Note:**

> thank u to everybody who participated in sanster week 2021 :)) 💙💜
> 
> come find me on [twitter](https://twitter.com/K8Maybe) or [tumblr](https://hyliantimelordin221b.tumblr.com/) if u would like :D
> 
> i do have more sanster week stuff to share!! i have been very busy though so i dunno when i'll get around to finishing it and posting :(( but it's all wartime sanster actually lol, and also one of them will have an illustration embedded that i commissioned from my very talented friend 👀 so there's that to look forward to ;p
> 
> also i jus wanna say for anyone stumbling upon this fic— if u like fucked-up sanster and/or sans suffering, u might enjoy most of my other fics as well 😳🙈 tho there’s some soft stuff sprinkled in there as well bc in this house we love All Flavors Of Sanster ᕕ( ᐛ )ᕗ 
> 
> if u comment i lov u

**Works inspired by this one:**

  * [Between Genius and Insanity](https://archiveofourown.org/works/29920044) by [QuintessenceA](https://archiveofourown.org/users/QuintessenceA/pseuds/QuintessenceA)




End file.
